Curable composition

Abstract

A curable composition is disclosed, including (A) an oxypropylene polymer having a narrow molecular weight distribution which does not have any branched chain, is linear and has at least one reactive silicon atom-containing group; and (B) an oxypropylene polymer having a narrow molecular weight distribution which has at least one branched chain and at least one reactive silicon atom-containing group. Cured articles obtained from the curable composition have a tear strength which is unexpectedly higher than the tear strength of the cured article of the component (A) alone or the component (B) alone.

What is claimed is: 
     
       1. A curable composition comprising: (A) an oxypropylene polymer:   (1) which has a ratio of Mw/Mn of not higher than 1.6;   (2) which has a polymer main chain consisting essentially of a repeating unit represented by the following formula; ##STR7## (3) which does not have any branched chain other than methyl groups of said repeating unit; and   (4) which has at least one silicon atom-containing group having one or more silicon atoms to which one or more hydrolyzable groups are attached; and   (B) an oxypropylene polymer:   (1) which has a ratio of Mw/Mn of not higher than 1.6;   (2) which as a polymer main chain consisting essentially of a repeating unit represented by the following formula; ##STR8## (3) which as at least one branched chain consisting essentially of a repeating unit represented by the above formula;   (4) which as at least one silicon atom-containing group having one or more silicon atoms to which one or more hydrolyzable groups are attached.   
     
     
       2. A curable composition as claimed in claim 1, wherein said silicon atom-containing group having one or more silicon atoms to which one or more hydroxyl groups or hydrolyzable groups are attached is a group represented by the following general formula ##STR9## wherein R 1  and R 2  each represents an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, an aralkyl group having 7 to 20 carbon atoms or a triorganosiloxy group of (R') 3  SiO-- provided that when two or more R 1  or R 2  groups exist, two or more R 1  or R 2  groups may be the same or different; R' represents a monovalent hydrocarbon group having 1 to 20 carbon atoms provided that three R' groups may be the same or different; X is a material selected from the group consisting of a hydroxyl group and a hydrolyzable group provided that, when two or more X groups exist, these X groups may be the same or different; a represents 0, 1, 2 or 3; b represents 0, 1 or 2; when two or more groups represented by the following formula ##STR10## exist, b in the above formula may be the same or different; and m represents an integer of 0 to 19 provided that the following relationship must be satisfied.   a+Σb≧1     
     
     
       3. A curable composition as claimed in claim 1, wherein said silicon atom-containing group is a group represented by the following general formula ##STR11## wherein R 2  represents an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, an aralkyl group having 7 to 20 carbon atoms or a triorganosiloxy group of (R') 3  SiO--; R' represents a monovalent hydrocarbon group having 1 to 20 carbon atoms provided that three R' groups may be the same or different; X is a material selected from the group consisting of a hydroxyl group and a hydrolyzable group provided that when two or more X groups exist, these X groups may be the same or different; and a represents 0, 1, 2 or 3. 
     
     
       4. A curable composition as claimed in claim 1, wherein said oxypropylene polymers (A) and (B) have a ratio of Mw/Mn of not higher than 1.5. 
     
     
       5. A curable composition as claimed in claim 1, wherein said oxypropylene polymer (B) is a polymer having one branched chain. 
     
     
       6. A curable composition as claimed in claim 1, further comprising a curing catalyst in an amount from about 0.1 to about 20 parts by weight of the composition. 
     
     
       7. A curable composition as claimed in claim 1, further comprising, per 100 parts by total weight of the oxypropylene polymers (A) and (B), about 5 to 20 parts of a filler, and from about 1 to about 100 parts of a plasticizer. 
     
     
       8. A curable composition as claimed in claim 1, wherein said oxypropylene polymers (A) and (B) have a number-average molecular weight (Mn) of not less than 4,000. 
     
     
       9. A curable composition as claimed in claim 1, wherein the mixing ratio, on a parts by weight basis, of said oxypropylene polymer (A) to said oxypropylene polymer (B) is from 10:90 to 90:10.